Hitherto, metal vapor deposited products, in which metal is vapor-deposited on plastic products, have widely been used as food containers and others since they have good decorative property, gas barrier property and light blocking property, and laminate films each obtained by vapor-depositing a silicon oxide film on a plastic film have been used for wrapping materials and others that have transparency and a high gas barrier property.
However, when they are made using, as a starting material thereof, a nonpolar polymer such as polypropylene resin or polyethylene resin, there arise problems that the adhesiveness between the polymer and a thin film vapor-deposited thereon is poor and the film is easily peeled.
In order to solve such problems, there is known a method of subjecting a plastic molded body or plastic film surface to physically surface-roughening treatment by corona discharge, flame radiation, radioactive ray radiation or the like and using anchor effect based on this treatment to improve the adhesiveness of the roughened surface to a thin film vapor-deposited. There is also known a method of applying a polar polymer such as polyester resin or polyamide resin onto the roughened surface and then vapor-depositing a metal thereon. However, even if such methods are used, the adhesiveness of the vapor-deposited thin film is insufficient.
Suggested is also a method of incorporating an additive into a plastic material, thereby improving the adhesiveness of the plastic to the film vapor-deposited thereon. Examples thereof include a method of incorporating, into polypropylene, a maleic anhydride modified polypropylene in which maleic anhydride is graft-polymerized (Japanese Patent Application Laid-Open (JP-A) No. 50-61469, and a method of incorporating magnesium oxide and magnesium silicate into a crystalline propylene-α-olefin copolymer (JP-A No. 8-104977).
However, according to these methods, it is difficult to disperse the additive uniformly. Consequently, unevenness is easily generated in the adhesiveness between the plastic material and the vapor-deposited film, and further the adhesiveness of the vapor-deposited thin film is unsatisfactory.
Meanwhile, attention has been paid to an amorphous carbon film as one of the above-mentioned thin films in recent years. The amorphous carbon film is an amorphous carbon film which does not clearly exhibit any crystal structure by X-ray analysis thereof, or a hydrogenated carbon film in which hydrogen is bonded to nonbonding hands of carbon, and is called an a-C:H film, an i-C film or a diamond-like carbon (DLC) film also.
The amorphous carbon film has a high hardness (Hv: 3000 or more), a good abrasion resistance, a good surface smoothness, a small abrasion coefficient, a good releasability, good chemical resistance/corrosion resistance, a good gas barrier property against oxygen, water vapor and other gases, a good transmittance to near infrared rays, a good electric non-conductance, and other physical properties close to those of diamond. Conditions for the film-formation thereof are simpler than conditions for that of diamond thin films; therefore, expectations that the amorphous film is used as a surface-treatment film for various substrates have been increasing.
Hitherto, as a method for forming an amorphous carbon film, for example, the following has been known: a method of gasifying a raw material containing carbon atoms in a vacuum by high heat so as to form an amorphous carbon film on a surface of a substrate. However, this method has a problem that the substrate is limited to a material having a high heat resistance, such as a metal or a ceramic, since the high heat is applied to the substrate.
In recent years, dry process technique for forming an amorphous carbon film has been advancing so as to make film-formation at low temperature possible. Thus, the application of the technique to surface treatment of polymer substrates has been advancing.
For example, JP-A No. 11-58587 discloses a laminate film having a gas barrier property in which an amorphous carbon film 0.1 μm in thickness is formed on a film made of polyethylene terephthalate; and JP-A No. 2001-49433 discloses a laminate in which an amorphous carbon film 2-3 μm in thickness having a high hardness and transparency is formed on a surface of a polar polymer such as polycarbonate or polymethyl methacrylate. However, in the case of using a nonpolar polymer such as polypropylene as a polymer substrate, the adhesiveness between this polymer substrate and an amorphous carbon film is poor to cause a problem that the film is easily peeled although the adhesiveness between the polymer as described above and the amorphous carbon film is relatively good.
For example, JP-A No. 2000-117881 discloses a gas barrier laminate in which an amorphous carbon film of 0.025 μm thickness is formed on an inside face of a container made of polypropylene; and JP-A No. 2001-310412 discloses a gas barrier laminate film in which an amorphous carbon film of 0.04 μm thickness is formed on a polyethylene film or a polypropylene film. These laminates have problems that the adhesiveness between the polymer substrate and the amorphous carbon film is poor, and further when the film thickness of the amorphous carbon film to be formed is desired to be made large, internal stress of the amorphous carbon film becomes large so that the film is easily peeled.